3 Answers
3

You probably misled the Windows utility by using extension tar on a gzipped file. As you're using gzip compression by using the -z flag, the common file-types are .tgz and .tar.gz. I have no idea whether or not 7-zip supports this. Alternatively you can drop the z flag.

Back in the days of yore when compression was still very expensive there was this program to backup data to tapes. It was called Tape ARchive. A tape device on unix is just a file, so it was also possible to dump this archive to a file. That file normally gets the extension .tar.

It you wanted to compress this a file (E.g. a freshly made backup) you used the program compress which added the extension .Z The resulting file then got both extentions. (file.tar.Z)

Later versions allowed you to combine these with the -z flag in tar. They also after substituted gzip for compress. The resulting gzip compressed tar file usually have the extension .tar.gz, or on some windows computers (due to 8.3 limitations) .tgz.